1. Field of the Invention
The present invention relates to a wafer processing method for dividing a wafer into individual devices along a plurality of crossing division lines formed on the front side of the wafer, the individual devices being formed in a plurality of separate regions defined by the division lines.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby define a plurality of separate regions where a plurality of devices such as ICs and LSIs are formed. The semiconductor wafer is cut along the division lines to thereby divide the regions where the devices are formed from each other, thus obtaining the individual devices as device chips.
Cutting of the semiconductor wafer along the division lines is usually performed by using a cutting apparatus called a dicing saw. This cutting apparatus includes a chuck table for holding a workpiece such as a semiconductor wafer and an optical device wafer, cutting means for cutting the workpiece held on the chuck table, and feeding means for relatively moving the chuck table and the cutting means. The cutting means includes a spindle unit having a rotating spindle, a cutting blade mounted on the rotating spindle, and a driving mechanism for rotationally driving the rotating spindle. The cutting blade includes a disk-shaped base and an annular cutting edge mounted on one side surface of the base along the outer circumference thereof. The annular cutting edge is an electroformed diamond blade formed by bonding diamond abrasive grains having a grain size of about 3 μm, for example, to the base until reaching a thickness of about 20 μm.
However, since the cutting edge of the cutting blade has a thickness of about 20 μm, each division line separating the devices must have a thickness of about 50 μm. Accordingly, the ratio in area of the division lines to the wafer is large, causing a reduction in productivity.
As a method of dividing a wafer such as a semiconductor wafer in recent years, there has been tried a laser processing method called internal processing of applying a pulsed laser beam having a transmission wavelength to the wafer along the division lines in the condition where the focal point of the pulsed laser beam is set inside the wafer in a subject area to be divided. More specifically, this wafer dividing method using laser processing called internal processing includes the steps of applying a pulsed laser beam having a transmission wavelength to the wafer from one side of the wafer along the division lines in the condition where the focal point of the pulsed laser beam is set inside the wafer to thereby continuously form a modified layer inside the wafer along each division line and next applying an external force to the wafer along each division line where the modified layer is formed to be reduced in strength, thereby breaking the wafer along each division line to obtain the individual devices (see Japanese Patent No. 3408805, for example).